Digital radio communications is one of the fastest growing services currently offered by the telecommunications industry. Within the field of digital radio communications, a relative newcomer is the packet transmission communications system.
Packet transmission systems have proven technically reliable and commercially valuable for the communication of information which occurs in bursts, such as computer data and digitized speech. The success achieved by packet transmission systems relates in part to the fact that the system's bandwidth is not continuously required by one communicator and thus may be shared by many via any of the well known multiple access schemes including, but not limited to Time Division Multiple Access (TDMA), Frequency Division Multiple Access (FDMA), Code Division Multiple Access (CDMA) and Space Division Multiple Access (SDMA). Also, packet transmission can be readily handled by modern digital equipment. For more on packet transmission systems, the interested reader may refer to U.S. Pat. No. 4,905,231 Leung et al. and U.S. Pat. No. 4,992,486 Lindinsky et al.
A number of packet transmission communication systems now exist in which a Node or controller communicates with a plurality of remote communication devices. Such systems include, but are not limited to:
the digital radiotelephone communication system, Group System Mobile (GSM), for use in Europe and defined in GSM documents GSM 05.01 "Physical Layer on the Radio Path: General Description" and GSM 05.02 "Multiplexing and Multiple Access On the Radio Path";
the voice and data communication system described in U.S. patent application Ser. No. 07/719,212, filed Jun. 21, 1991, entitled Voice and Data Packet Communication Method and Apparatus, as assigned to the assignee of the present invention; and
the digital radiotelephone communication system, Digital European Cordless Telecommunications (DECT), for use in the European Personal Communications arena, as described in the following articles:
C. Van Diepenbeek, "DECT, A GENERAL OVERVIEW", Fourth Nordic Seminar on Digital Mobile Radio Communications DMR IV, Oslo; 26-28 June 1990; PA0 A. Bud, "SYSTEMS & NETWORK ASPECTS OF DECT", Fourth Nordic Seminar on Digital Mobile Radio Communications DMR IV, Oslo; 26-28 June 1990; and PA0 Dr. H. Ochsner, "RADIO ASPECTS OF DECT", Fourth Nordic Seminar on Digital Mobile Radio Communications DMR IV, Oslo; 26-28 June 1990.
Each of the above-listed systems is characterized by a defined set of operating frequencies and distinguished by a distinct air interface, hereinafter referred to as a transmission protocol, no two of which are exactly alike. For example, FIG. 1 depicts the data structure of a GSM burst transmission 100. Each GSM burst transmission consists of one hundred and forty eight (148) bits which are transmitted at a rate of 270.833 kilobits/second. One hundred and fourteen (114) of these bits 110 are available for actual data transmission, the rest are used to assist reception and detection of the burst 100. A training sequence in the middle of the burst, referred to as the synchronization signal pattern or Synch Word 120, is used to estimate the radio channel impulse response and to assist in the synchronization of a receiver's operations. Three header or tail bits 105 at either end of a burst delimit the begin and/or end of a burst. Finally, two stealing flags 115 immediately before and after the Synch Word 120 indicate that a burst which originally had been assigned to a traffic channel was "stolen" to be reassigned for signalling purposes.
In contrast, FIG. 2 depicts the data structure of a DECT burst transmission 200. Each DECT burst transmission consists of four hundred and twenty (420) bits which are transmitted at a rate of approximately 1152 kilobits/second. Three hundred and twenty (320) of these bits 220 are available for actual data transmission, the rest are used to assist reception and detection of the burst 200. A training sequence 205 at the head of the burst 200, referred to as the synchronization signal pattern or Synch Word, is used to assist synchronize a receiver's operation. Forty Eight bits 210 facilitate the multiplexing of DECT Logical Channels. Thereafter, sixteen bits 215 provide a Cyclic Redundancy Check (CRC) function, used to verify the correctness of the received data. Finally four bits 225 are used to recognize radio interference of the received data.
FIG. 3 depicts the data structure of a burst transmission 300 utilized by the packet transmission communication system described in U.S. patent application Ser. No. 07/719,212, filed Jun. 21, 1991, entitled Voice and Data Packet Communication Method and Apparatus. The format consists of a training sequence 305, referred to as the synchronization signal pattern or Synch Word, a packet header field 310 and data field 320. As previously discussed, the Synch Word 305 is provided for synchronization purposes. The packet header 310 will be explained in more detail below. The data field 320 represents the information to be communicated between users.
FIG. 4 illustrates the information contained within the packet header 310 of FIG. 3. The header 310 includes a virtual circuit identification field 311, a packet length field 313, destination information field 315, and a validation information field 317. The virtual circuit identification field 311 contains information that specifies a register address which holds control information that directs where the data field 320 of a burst transmission 300 is stored in memory. The packet length field 313 provides information concerning the length of the data field 320. The destination information field 315 contains the intermediate destination address information which determines if the data field 320 is stored in memory. Finally, the validation information field 317 contains data associated with a CRC data accuracy calculation.
From the foregoing, it is apparent that communications equipment (radios) designed to operate utilizing the GSM format and associated frequencies will be incapable of accessing or communicating with communications equipment designed per the DECT specification. The same is true for other radio communications equipment designed for systems which either operate on differing communications channels or employ incompatible transmission protocols. Such systems include, but are not limited to: the UK's Personal Communications Network (PCN), also referred to as DCS1800, the United States Digital Cellular System (USDC), Japan's Digital Cellular System (JDC) and the like.
In light of the incompatible nature of existing packet transmission communication systems, and in recognition of the modern trend toward compatibility, it would be extremely advantageous to provide a common communications Node which is capable of supporting a variety of different radio-types, i.e., a plurality of different communications systems.